For example, PTL 1 discloses a device that includes a radar sensor in a vehicle and acquires the lateral width of an object as a lateral dimension from a reflection point on the object by the radar sensor. The device described in PTL 1 determines that the true value of the lateral width is not detected when the object is positioned at an end of the probe range of the radar sensor or when another object exists in front of the target object. When determining that the object is not detected, the device corrects the current lateral width by a past lateral width recorded in a history.
According to PTL 1, even when the lateral width of an object is not correctly detected, the lateral width is corrected based on the past history information to suppress a problem that a warning or the like is given due to a failure to acquire the correct lateral width.